shaved head tech

[TurboFlush]

ok, I finally got around to putting the adjustable pulley on. I was suprised at how much the cam was off. I had the head shaved to the max. the cam looks to be off about 5 degrees advanced (I think it was). after setting the cam closer to originall the car ran better.
I then retarded it some more just to see what would happen. it seemed to run a litlle worse. hard to test though at 0200 in the morning when everyone is asleep.

Now I have been told that the came timing shouldnt matter. but I believe it is depending on the cam. I am using a slightly worn cam from a EFI motor for a carb setup. I am guessing with this cam it needs to be close to originall setting. although at whatever position it was at it had better top end, but it was to high for my taste (7k rpm).

Since I want to sell the car, I plan on keeping my adj pulley. I will find out where it runs best and weld up the slot on the originall and re cut it to where I need the key way to be.

TF

 

[Ray III]

I ought to check my cam timing cuz I took .060" off the head and it aint got near the power it ought to, and a bit bumpy of an idle. I looked the marks over 3 times, they looked DEAD on but maybe I am missing a couple degrees after all.

When you shave the head does that tend to bias the cam more for higher RPM torque peak, or lower RPM? I'm hoping the former, so I can lust leave it alone and open up the intake for more power.

 

[Willy0314]

im a little confused at how shaving the head actually would alter cam timing. Especially since the cam is bolted right on to the head of these motors. Unless maybe it has something to do with how it would take a shorter belt, because the distance between the crank and cam pullies is now shorter, except there has to be something to tension the belt right?

 

[bhuff30]

your close. When you mill the head, the tensioner does take the slack, but since it can only take out the slack on one side, the cam has to rotate slightly for the tensioner to take up the slack.
I calculated this out once, and got 2* for every .100 you mill off. The 5* of advance you had is probably just the difference of intake lobe centerline or manufacturing tolerances.

 

[Willy0314]

ahhhh now it makes sense

 

[TurboFlush]

I was going to devise a way to place a idler on the other side to turn the cam back. but I think it will be easier just reslotting a sprocket for the cam.
like said above, the belt turns the cam counterclockwise (I believe retarded). before with the normall cam sprocket on there the 5 deg of extra timing (on the sprocket) was causing it to ping whenever I got on it in second gear. It seems to be that with the shaved head and the originall sprocket it gives it a stronger top end. but it is such a high top end that it is useless.
I will try and post some pics and a writeup lateron.

TF

 

[Willy0314]

hmmmm....the only thing is, you would need the seccond idler to have the exact same amount of pull on the belt as the stock one dose. Other wise it will still be out. ya know what i mean? I think that the adjustable cam sprocket might be the easiest way to go. Even if you have to bust out a Die-grinder to enlarge some slots, so you can get more adjustment out of it.